<!DOCTYPE html>
<html>
  <body>
      <p id="demo">Hello JavaScript！</p>
      <button type="button" onclick="myFunction()">开始</button>
      <input type="button" value="隐藏文本" onclick="document.getElementById('demo').style.visibility='hidden'" />
      <input type="button" value="显示文本" onclick="document.getElementById('demo').style.visibility='visible'" />
      <script src="hello_world.js"></script>
  </body>
</html>